In recent years, 3GPP (3rd Generation Partnership Projects) has specified a mobile communication system employing a “W-CDMA (Wideband-Code Division Multiple Access) scheme or UMTS (Universal Mobile Telecommunications System) scheme” based on CDMA (Code Division Multiple Access) techniques.
A mobile communication system of the W-CDMA scheme includes a “DHO (diversity hand over) function” as a radio layer protocol function.
The DHO function is a function to allow a mobile station (UE: user equipment) to perform communication through a radio data link established with multiple cells managed by a radio base station, and to achieve maximization of a gain and stabilization of communication by using a maximum ratio combining process, a selection combining process, and the like of received data.
Here, a radio control station is configured to perform such a control as to disconnect a radio data link established between a cell having deteriorated communication quality and the mobile station UE on the basis of a request from the mobile station UE, or on the other hand, to add a radio data link between a cell having a good communication quality and the mobile station UE on the basis of a report from the mobile station UE.
Moreover, in the mobile communication system of the W-CDMA scheme, the radio control station not only performs the above-described control at the time of movement of the mobile station UE but also starts communication between the mobile station UE and multiple cells having a good communication quality in a DHO state when a communicate is possible between the mobile station UE and the multiple cells having a good communication quality. Thereby, radio resources can be used effectively.
As shown in FIG. 1, there has heretofore been known a mobile communication system in which multiple areas A and B are formed by multiple radio base stations 01 and 02 and a radio control station 10, and a particular service is offered in the area A.
For example, according to the above-described communication system, a particular service such as a flat-rate communication service for a specific contracted user is offered in the area A.
However, according to the above-described mobile communication system, if the mobile station UE moves out of the area A, then it is not possible to continue to offer the particular service in the DHO state to the mobile station UE unless the same particular service as in the area A is offered in an adjacent area (hereinafter referred to as the area B) to the area A.
For this reason, in general, when the radio control station receives a branch addition request from the mobile station UE while a particular service is offered (such as an extension communication service) to the mobile station UE through a certain radio data link (hereinafter referred to as a branch), the radio control station is forced to execute such a control as to suspend the offer of the particular service to the mobile station UE if the particular service cannot be offered via the branch involved in the branch addition request.
As a result, it is assumed likely that interference of the area B at an edge of the area A causes the branch addition request concerning a cell in the area B to be transmitted from the mobile station UE. If the area B is the area which does not offer the particular service, then it is likely that the mobile station UE cannot continue to use the particular service, even through the mobile station UE is located in the area A.
Meanwhile, if the mobile station UE also establishes the branch with the cell in the area B being the area not offering the particular service (the branch which cannot offer the particular service) when starting communication concerning the particular service in the area A being the area offering the particular service, then the mobile station UE is unable to use the particular service. Therefore, broad coverage of the area offering the particular service cannot be ensured.
Here, for example, in order to maintain continuity of communication concerning the particular service even at the edge of the area A offering the particular service, the same particular service needs to be offered in the area B which is adjacent to the area A being the area offering the particular service.
As a result, it is possible to reduce an effect of the interference with the adjacent area B at the edge of the area A offering the particular service, and to allow the mobile station UE to use the particular service in the DHO state.
As described above, according to the conventional mobile communication system, the area offering the particular service becomes too broad when the adjacent area to the area offering the particular service is also configured to offer the same particular service, and an operating company cannot limit the area offering the particular service within an originally intended area (such as an indoor area). Hence the conventional mobile communication system has a problem that there is a possibility of causing pressure on a communication capacity attributable to an increase in communication related to the particular service in an area outside the area originally intended by the operating company (such as an entire outdoor area).
Moreover, the conventional mobile communication system has a possibility to cause a difference related to the broad coverage of the area offering the particular service or a temporal change of the area offering the particular service for each mobile station UE depending on a difference in the configuration of each area offering the particular service or on a change of the area offering the particular service. Since the operating company cannot control these factors, there is a problem that a service quality of the particular service may be impaired.